In a process of building physical abilities, athletes temporarily experience underperformance after heavy training. However, their physical abilities improve during a process of recovery from fatigues caused by the training. This phenomenon is known as super recovery. If the athletes continue heavy training without rest, fatigue builds up and may result in injury when a level of the fatigue exceeds their fatigue limit. Athletes are more likely to develop a physical disorder called an overtraining syndrome under such conditions. Physical abilities improve or degrade according to fatigue or recovery as shown in FIG. 10.
The overtraining syndrome is a phenomenon that athletic abilities of athletes decrease due to lack of balance between training load and rest. Symptoms of minor injury are difficult to distinguish from fatigue. If the minor injury is not noticed and the training is continued, the symptoms of minor injury may become worse. As a result, the athlete may fall in a serious physical condition, from which it is difficult to recover. It may take over a year for an athlete to recover from serious injury while it normally takes a few days to recover from minor injury. Therefore, it is very important to properly monitor physical conditions of athletes to prevent overtraining.
The amount of training, the amount of rest, and the performance of athletes during training are usually used as indexes for determination of overtraining. However, it is difficult to detect overtraining based on these indexes because an ability to cope with fatigue, a fatigue limit, or a level of recovery differs from athlete to athlete. Namely, it is difficult to determine overtraining based on standardized indexes and the overtraining determination greatly depends on experiences of trainers.
To objectively determine a level of recovery or a level of fatigue, heart rate, or pulse rate, and temperature after waking up in the morning are used as indexes in addition to the above-described indexes. However, such heart rate and the temperature greatly vary according to a wake-up condition, for instance, waking up in hurry or frightened by an alarm clock. Thus, accurate determination of levels of rest and recovery after sleep cannot be made based on the heart rate and the temperature after waking up.
An apparatus for detecting overuse of muscles of lower limbs is proposed in JP-A-11-137539. In this apparatus, shock absorbing capabilities of the lower limbs during running are measured and overuse of the muscles is determined based on a decrease in the capabilities. Namely, it only determines whether temporary fatigue in the lower limbs during training exceeds the limit but not properly detect signs or symptoms of overtraining resulting from an accumulation of fatigue.
The sufficient amount of rest is required before starting training again when an athlete has recovered from overtraining. Thus, it is important to understand a level of recovery of the athlete from the overtraining. However, the level of recovery is not accurately detected by known methods.